Changing from smart trainer to power meter. How to work the differences?


I’ve just installed a spider-based power meter - where the data I’ve been recording since December has been with a Kickr Snap wheel-on trainer.

I haven’t done a proper comparison yet - only run the two together for 15 minutes and eyeballed the two power values. But it looks like the FSA meter is about 10-20 watts higher than the Kickr. It may be drivetrain loss, an inherent issue with one of the devices etc but I want to now base my power on the FSA power meter so I can include power data from outside - rather than used derived values.

The issue I have is what I should do to get my Kickr-based Fitness Signature accurate? I’m in ‘base’ with no decay, so not pushing for breakthroughs. By following the prescribed activities, I think I’m going to be riding below what I should be on?

Should I go all out for a few breakthroughs? Should I start locking activities as a starting point?

Any advice welcome.


Hey Steve, I went through the same situation last year. In my case I was using a Tacx Vortex for power and added some Assioma DUO pedals and switched to using them as my power meter. I experienced the opposite though, my power values dropped by ~20 W. I ended up allowing my fitness signature to slowly recalibrate over a month.

Now that I understand more about XERT I think I could have just followed the instructions on the Fitness Signature Calculator and done three best effort rides and input that info into the Power Duration section to generate a more accurate Fitness Signature.

Thanks - I did a proper comparison and they look near enough the same :frowning: boo - thought I had a few extra free watts to the TP there.